Balrog of Morgoth

...Something was coming up behind them. What it was could not be seen: it was a great shadow, in the middle of which was a dark form, of man-shape maybe, yet greater; and a power and terror seemed to be in it and to go before it...It came to the edge of the fire and the light faded as if a cloud had bent over it. Then with a rush it leaped across the fissure. The flames roared up to greet it, and wreathed about it; and a black smoke swirled in the air. Its streaming mane kindled, and blazed behind it..."What is this new devilry", fear fell over the son of Thuranduil.  "A Balrog", Gandalf returned. "A demon of the ancient world. This foe is beyond any of you.  Lead them on, Aragorn. Do as I say! Swords are no more use here!  Over the bridge!" cried Gandalf, recalling his strength. "Fly! This is a foe beyond any of you. I must hold the narrow way. Fly!" Aragorn and Boromir did not heed the command, but still held their ground, side by side, behind Gandalf at the far end of the bridge. The others halted just within the doorway at the hall's end, and turned, unable to leave their leader to face the enemy alone...The Balrog reached the bridge. Gandalf stood in the middle of the span, leaning on the staff in his left hand, but in his other hand Glamdring gleamed, cold and white. His enemy halted again, facing him, and the shadow about it reached out like two vast wings. It raised the whip, and the thongs whined and cracked. Fire came from its nostrils.  But Gandalf stood firm
"You cannot pass!" Gandalf said defiantly.  "I am a servant of the Secret Fire, wielder of the flame of Anor. You cannot pass. The dark fire will not avail you, flame of Udun. Go back to the Shadow! You cannot pass."  The Balrog made no answer. The fire in it seemed to die, but the darkness grew. It stepped forward slowly on to the bridge, and suddenly it drew itself up to a great height, and its wings were spread from wall to wall; but still Gandalf could be seen, glimmering in the gloom; he seemed small, and altogether alone: grey and bent, like a wizened tree before the onset of a storm.From out of the shadow a red sword leaped flaming.  Glamdring gleamed white in answer. There was a ringing clash and a stab of white fire. The Balrog fell back and its sword flew up in molten fragments. The wizard swayed on the bridge, stepped back a pace, and then again stood still...